Safety report reveals details behind what caused a 13m sinkhole to open up at WA mine site

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Four workers were lucky to escape serious injury when a massive sinkhole swallowed two vehicles — including an explosives truck — and equipment at a WA mine site late last year.

A Department of Mines, Industry Regulation and Safety report into the October “significant incident” released on Friday said the pit floor had subsided into a backfilled stope, forming the 13m-deep hole.

The explosives truck and integrated tool carrier, both unoccupied but parked on the blast pattern, fell into the void.

The department did not disclose the location of the mine or the name of the companies involved but it is understood the incident happened at the Gossan Hill open pit at Golden Grove’s polymetallic mine 250km east of Geraldton.

Camera IconThe wreck of vehicles at the bottom of the sinkhole.Picture: DMIRS

The report noted the area had been backfilled in stages since 2016 and surface drilling and blast activities were under way in the vicinity at the time.

“A number of charged blast holes were also engulfed in the sinkhole. The vehicles were unoccupied at the time of collapse; however, four persons were working in close proximity,” the department said.

The report said the backfilled workings had not been treated as a “void” and work was allowed to continue “above an area of unknown stability”.

It also noted a risk assessment in December 2017 had identified the void as a hazard but said recommended controls were not followed.

“The decision was made in July 2018 to move from strict void management protocols to standard mining practices on the (incorrect) assumption that the pre-2018 backfilled section of the stope void was tight-filled,” it said.

The report made a number of recommendations and the department said its investigation into the incident was ongoing.